Rail for a window covering



FIG. 1 is a perspective view of a rail for a window covering showing my new design;

FIG. 2 is a left end view thereof, which is the same as the right end view thereof;

FIG. 3 is a front view thereof, which is the same as the rear view thereof;

FIG. 4 is a top view thereof; and,

FIG. 5 is a bottom view thereof.

The broken line in the figures is a cut-line and forms no part of the claimed design. Any portions of the rail for a window covering that are not shown in the drawings form no part of the claimed design. 

CLAIM The ornamental design for a rail for a window covering, as shown and described. 